This is probably not the right thread for me for reasons that might be indicated below, but why not, I'll nibble.
Fandoms?
Mmm. I like Diablo, Battletech, Starcraft, Elder Scrolls, old era Game of Thrones, Star Wars, and a couple very niche contexts.
Pairings?
Not many. I seriously dislike 'shipping', the seemingly whimsical what-ifs that pair characters together romantically, and often damn the source material. I don't like getting into contexts where I'm not intimately familiar with the source, which is why I straight up don't pick up things outside of the niches I like to the point where I'm willing to research and immerse. That said, some sort of romantic connection between Leah and someone (likely the Nephalem) in the Diablo context and even a couple other scenarios in the same game root are things that legitimately interest me. I think she had a shot at being closer with someone on a character and story level, and I think she was cheated out of depth. So it's still a thing high in my interests, and I know it's reliable when I've had an idea in my head for a rather long time.
Genres?
I'm partial to fantasy, but I rarely take a stab at modern and occasionally get into Sci-Fi, emphasis intended. BT is the only context where I just like the sci part despite not having much fi, and that's from basically childhood influences. But for contexts those'll do it. On other matters I like darker, grimmer contexts; less LOTR, more GOT in nature, my own stuff is something of a cross that leans one way or another depending on the specific part.
I don't go to the site for the fourth question, sorry.
Authors?
GRRM's pretty big for me. In practice my writing is something like Stephan King (in structure) crossed with Tolkien without the depth, because I'm actually a very clumsy writer and think too far in abstract. I ultimately like all three, but I tend to judge more on specific work than author, so that variable isn't too key for me (despite, yes, authors tending to leave their style/mark on whatever they make - it's the same weirdness that makes me care so much more for characters in, say, movies than who the actor is behind them unless the quality distinction is too large).
Ratings?
I don't typically run off towards reading smut unless I want something for inspiration in my own writing, but typically I am not a child friendly reader. Be it horror (psychological especially), outright adult themes and concepts relating to violence, sex, and so on, or just plain heavy material, I am all across the mature/explicit/unrated spectrum, but rarely back into PG.
Crossovers? (Or do you hate them?)
Eeeeeh... generally a no for execution reasons, and some mainstream examples leave a meh taste in my mouth when they start crossing things over. I think it can be done well, but I haven't been pleased by them in any execution, and I feel singular materials are often incredibly underrated for the potential they have even if they're small or even not very fleshed out.
AU or nah?
Legit depends. Usually? Nah.
To be contrarian, I actually like the limitations of an existing canon. For one, it gives me something to research; to better portray the content, the values, the vision, offering me the ability to diversify my approach rather than bend something to my singular tastes. In a lot of ways I'm ignorant. I've tried to change that, but it's stuck, and playing true to a canon allows me to diversify. I prefer an intimate knowledge of a context to simply skipping towards 'what if I put this in this context'. There's enough of that out there, and while I used to kinda like it, I also used to try and do 5000000 things at any given time across work and hobbies, and I'm trying to tone it down. I'm trying to stick to consistency in what I enjoy, and I find staying true to a context rather than splitting it leaves me more 'free' to explore certain concepts and narratives within an accurate representation of the source. Not as common and something I certainly enjoy.
There's more to it than that, but I'd just be rambling and I don't expect this to go far, so I leave it at that.
An AU for me comes when I review content and decide a) it's not very good in general or b) I in particular don't like it but think it could be better with fundamental changes. Again to stand at odds, I think the sequel trilogy for star wars would fit neatly in this camp, if I hadn't long decided that limiting myself to the skywalker era just wasn't very enjoyable. Hey, I like authenticity, but I have to like the source first. I never cared terribly much for post ROTJ stuff, and the latest movies just solidify that. But that's neither here nor there. In a roleplaying context I would be willing to go for 'AUs' that change up characters/premise on Game of Thrones, purely for critical review on Star Wars (since my only investment really came from seeing how the new generation is handled and going 'good god'), Battletech post Jihad era potentially, and both Diablo and Starcraft - both I feel were terribly underutilized in their story potential.
What I otherwise do isn't really AU at all, but rather expanding the source material. I like doing that for one-off games that have an interesting premise but no real background. Some old games and a couple new projects fit this camp. A game like didnapper falls strongly here.
Occasionally I take the broad contexts implied by a game and use the sandbox environments to create an AU of the period that isn't bound by nation, deep history, or developments per real world logic, and instead try to fit what results with new logic that may be a bit abstract, but still functional, even with some depth. I did this a lot on an old ww2 game that had an editor to create a weird world scenario thing and very extensively in a few total war games, one in particular, where I'd use world maps, turn them to AI, let them go a few hundred turns and then hop in to see what happened. The results give me surprisingly vast material to work with. I'd ramble more if I had an outlet, but for the most part I'm just content that it's a thing.
I guess I just like making something from (almost) nothing rather than continue on with something that feels unpleasant.
All in all though, I don't really care to do AU as it's usually interpreted in the fandom audience.
Pairings you can’t stand?
Anything I feel doesn't correspond well with character portrayals.
...gonna dip back into the lava again and say this pretty much takes me out for most interests regarding new gen Star Wars, Overwatch, and while I haven't gone too much farther out, basically any contexts where people shoehorn characters into relationship roles (starting at just friendship or straight up enemies, genderbending/shifting their source to fit, so on) and go 'but it would be fun!'. Yeah, I guess, and I'm not around to take that away. But for me? I pass.
Bad tropes?
Like above I think it's a matter of execution, but 'trend sniffing' gets on my nerves. One kinda under the radar example is when I saw virtually every demon character be a human with powers and wings. Ugh. It's not just that, there's kind of a checklist in my mind that identifies that kind of character, but my specific interest in demon characters paired with a general disinterest in anything that can be blanketed under anime leaves me really turning my nose at the type. Diablo, Lovecraft, and other contexts being my influence don't help either.
Things that immediately turn you off reading something or themes you hate?
I hinted them, but I'll summarize them.
- Character bent to fit a spot. I got really obsessive over character accuracy a few years back (though it's always been my thing) and now I'm downright just bleh for it.
- Theme over story. I feel a story and its characters should always be a key thing, governed in roleplay only by OOC factors that are established before the play begins and followed up by adjustments that are friendly to the content that follows. In basically any work, I'm immediately turned off if the story panders to a theme, a message, so on and so forth at the expense of itself. It's why I have no problem with diversity in filmmaking for example, but get a bit antsy when it's clear or stated that the reason is for its own sake. Likewise, something doing that in a context where it's appropriate should be getting praise. I feel people get too caught up in the one or the other extremes.
- I don't like it when something goes off trying to be subversive 'because', or favors cheap twists, commits a total tonal change to the material (especially if it's set in existing material), or is whimsically bending backwards to what is desired OOC. I want to follow the character. I don't write too long or too well, but I take pride in what I make fitting what is supposed to happen, as long as I keep a clear image of what's going on and respond to the right stimulus.
- Structurally/grammatically bad. Maybe an irony, but I do have limits.
I should probably disclaimer and say yes, I do indeed know that characters don't do the same things depending on their emotional state, the background variables, in accordance to simple character logic every time, or in accordance to logic in general. People who are established as doing things a certain way are completely able to do a 180 and do something then perceived as 'out of character'. It gets blurry when trying to judge someone on that basis. Still, I think appropriately understanding a character allows a player to get into the 'gut feelings' and decide if that's what would be right. And that's part of roleplay to me. I haven't gone terribly deep on this site for any of that, but it's still a deep interest. Being able to explore this stuff and immerse in identities foreign to my own is part of why I dislike straying from canon portrayals on things I like. Just because it's canon doesn't mean it can't be creative, original, unique or interesting, and likewise, favoring canonical accuracy doesn't boil down to getting on someone's ass over every decision they make with that alias. Personally, I'm far more lax in judging other's portrayals than I am judging my own.
Fanfiction for me is a funny thing. I don't like it the way most people do. Its main influence on me comes from personally fleshing out stories on games I played way back when. I've always been an odd one. While I have done quite a bit with existing contexts, far more of my time has been spent on original work. But I consider most original work to just be the sum of influences, which naturally come out of other creations. By immersing in what exists I gain ideas for what to construct in my own content and, hopefully, end up doing a better job as a result.